Joshua,

I have many clients on Sonicwalls without issue with Avast for Business. Unless you have changed the default rule for LAN > WAN is to allow. You do not need any WAN>LAN rules as the client polls the console and the console makes no inbound connections.

I believe in the firewall rules section there is an option for a “Matrix” view then pick LAN > WAN and check the rule(s) shown.

Let us know if you need further assistance with this!

Cheers,
Mac